Process for preparing dialkylnaphthalene

ABSTRACT

A process for producing alkylnaphthalene from a feedstock comprising isomers of dialkylnaphthalene and naphthalene by contacting the feedstock with a catalyst composition, in which the process comprising transalkylation between isomers of dialkylnaphthalene and naphthalene to produce monoalkylnaphthalene, and isomerization of dialkylnaphthalene, wherein the catalyst composition comprising a synthetic zeolite characterized by an X-ray diffraction pattern including interplanar d-spacing as set forth in Table A of the specification.

This is a Division, of application Ser. No. 08/661,114 filed on Jun. 10,1996 now U.S. Pat. No. 5,744,670.

FIELD OF THE INVENTION

This invention relates to a process for preparing alkylnaphthalene, andparticularly to a method for preparing 2,6-dimethylnaphthalene(DMN) fromnaphthalene with an alkylating agent by using catalysts in bothtransalkylation and isomerization of DMN, as well as in alkylation ofmonomethylnaphthalene(MMN). This process is hereinafter describedspecifically by the preparation of 2,6-DMN, however, this process can beextentable to any dialkylnaphthalene.

BACKGROUND OF THE INVENTION

The compound 2,6-DMN is used as a precursor of2,6-naphthalenedicarboxylic acid in the manufacture of polyester resins,because 2,6-DMN is easily oxidised to 2,6-naphthalenedicarboxylic acidcompared with other precursors such as 2,6-diisopropylnaphthalene or2-methyl-6-isobutyrylnaphthalenes.

There are a lot of proposal concerning the process for preparing the2,6-DMN.

U.S. Pat. No. 4,795,847 (Weitkamp et al.) describes a process for thepreparation of 2,6-dialkylnaphthalene by alkylating naphthalene or2-alkyl-naphthalene with an alkylating agent in the presence of azeolite (specifically ZSM-5) as a catalyst.

U.S. Pat. No. 5,001,295 (Angevine et al.) describes process forpreparing DMN by using 2-MN and naphthalene as a feedstock and asynthetic zeolite (MCM-22) as a catalyst, and it shows MCM-22 is moreeffective than ZSM-5 in alkylation of 2-MN and naphthalene.

However these conventional arts provide only unit operation foralkylation of 2-MN, which is an expensive feedstock and is not availablein a large amount commercially. In addition, there is no descriptionconcerning how to use the DMN mixture(2,6-poor-DMN) after separation of2,6-DMN, and the productivity of 2,6-DMN is not sufficient for massproduction.

To increase the productivity of 2,6-DMN, it is preferable to utilize andisomerize 2,6-poor-DMN to enrich 2,6-DMN in DMN isomers.

In order to utilize the 2,6-poor-DMN isomers effectively, the JapanesePatent Laid-Open No.4-1142 shows a process to recycle the 2,6-poor-DMNisomers for isomerization, and combines transalkylation between of the2,6-poor-DMN isomers with naphthalene to produce MMN. Produced MMN isalkylated with alkylating agent to produce DMN.

This process consists of 5 steps (1)˜(5);

(1) 1st step (transalkylation and isomerization based on a modifiedZSM-5 as a catalyst)

DMN+NL→MMN

DMN filtrate→2,6-rich-DMN isomers

(2) 2nd step (separation of the product of the 1st step intonaphthalene, MMN and DMN by distillation)

(3) 3rd step (methylation of MMN using methylating agent to produce DMN)

MMN+methyl unit→DMN

(4) 4th step (separation of the product of the 3rd step into MMN and DMNby distillation

(5) 5th step (separation of 2,6-DMN from the DMN mixture of the secondstep and the 4th step by cooling crystallization)

According to the process, 2,6-poor-DMN isomers can be enrich 2,6-DMN atleast to some extent. However yield of 2,6-DMN is still low.

The reasons of low yield of 2,6-DMN in the conventional process isconsidered to be based on the following two difficulties.

difficulty of the effective isomerization

Ten isomers of DMN can be categorised into the following four groups(i)˜(iv).

(i) 1,4-DMN1,3-DMN2, 3-DMN

(ii) 1,5-DMN1,6-DMN2,6-DMN

(iii) 1,8-DMN1,7-DMN2,7-DMN

(iv) 1, 2-DMN ##STR1##

Isomerization within each groups is easily proceeded, however theisomerization beyond groups is very difficult to be carried out. It isdue to the polarity of the naphthalene molecule which allows themethyl-transition between α-position and β-position (e.g.1,5-DMN⃡1,6-DMN), however transition between β-position and β-position(e.g. 2,6-DMN⃡2,7-DMN) with the ring is not allowed easily. That is whyisomerization of 2,6-poor-DMN isomers is not effective to enrich2,6-DMN. In the above-mentioned Japanese Patent Laid-Open No. 4-1142,low catalyst performance in the transalkylation and the alkylationcauses the low separation yield of 2,6-DMN from DMN isomers.

Therefore, it is very important to use a catalyst which has highselectivity of 2,6-DMN in isomerization.

difficulty in separation of 2,6-DMN from DMN isomers

Furthermore it is very difficult to separate 2,6-DMN from other isomersby conventional separation methods such as distillation or coolingcrystallization owing to the presense of 2,7-DMN.

In the distillation, 2,6-DMN and 2,7-DMN can not be separated each otherbecause the difference of boiling point between 2,6-DMN and 2,7-DMN isonly 0.3° C.

As for the cooling crystallization, since 2,6-DMN and 2,7-DMN forms aneutectic crystal at the weight ratio of 0.7(=2,6-DMN/2,7-DMN) the onlylow yield of 2,6-DMN is achieved. For example, according to theabove-mentioned Japanese Patent Laid-Open No. 4-1142, the ratio of2,6-DMN/2,7-DMN is 1.0. That is why the yield of 2,6-DMN is not high.

Consequently it is very important to increase the ratio of2,6-DMN/2,7-DMN for the higher yield of 2,6-DMN.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoing situationand it intends to provide a process for preparing usefulalkylnaphthalene such as 2,6-DMN at a high yield.

Provided herein is a process for producing alkylnaphthalene from afeedstock comprising isomers of dialkylnaphthalene and naphthalene bycontacting said feedstock with a catalyst composition, said processconsisting essentially of transalkylation between isomers ofdialkylnaphthalene and naphthalene to produce monoalkylnaphthalene, andisomerization of dialkylnaphthalene, wherein said catalyst compositioncomprising a synthetic zeolite characterized by an X-ray diffractionpattern including interplanar d-spacing as set forth in Table A.

                  TABLE A                                                         ______________________________________                                        interplanar d-spacing                                                                        relative intensity                                             (Å)        I/I.sub.0  × 100                                         ______________________________________                                        12.36 ± 0.4 M--VS                                                          11.03 ± 0.2 M--S                                                           8.83 ± 0.14 M--VS                                                          6.18 ± 0.12 M--VS                                                          6.00 ± 0.10 W--M                                                           4.06 ± 0.07 W--S                                                           3.91 ± 0.07 M--VS                                                          3.42 ± 0.06 VS                                                             ______________________________________                                         *The relative intensities are given in terms of the symbols;                  W = weak, M = medium, S = strong, VS = very strong.                      

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a schematic diagram to show preferable process of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventors have made earnest studies to higher the yield of2,6-DMN, as a result, have accomplished the present invention based onthe finding the the ratio of 2,6-DMN/2,7-DMN can be increased more than1.2 by employing a particular catalyst in the transalkylation andisomerization of 2,6-poor-DMN, as well as alkylation of MMN.

The particular catalyst is a zeolite which comprises a synthetic porouscrystalline material characterized by an X-ray diffraction patternincluding interplanar d-spacing can be set forth in the Table A.

The zeolite is known as MCM-22 and the entire contents of applicationSer. No. 5,001,295 are incorporated herein by reference.

Transalkylation and isomerization conditions include a temperature ofbetween about 0° to 500° C., and preferably between 240° and 450° C.,and pressure of between 0 to 250 atmospheres and preferably 1 to 25atmospheres. The mole ratio of naphthalene to DMN can be from about 1:1to 1:10 and preferably can be from 1:1 to 1:5. The reaction is suitablyaccomplished utilizing a feed space velocity of between about 0.1 to10.0 hr⁻¹.

In the transalkylation and isomerization of the present invention,2,6-poor-DMN which contains less than 11 weight % of 2,6-DMN in theisomers is preferred as isomers of DMN in the feedstock, more preferablycontent of 2,6-DMN is less than 9%.

As mentioned above, a high ratio of 2,6-DMN/2,7-DMN is required toobtain high yield of 2,6-DMN. According to the present invention, theratio of 2,6-DMN/2,7-DMN can be more than 1.2.

Further, the performance of catalyst in isomerization can be evaluatedby a molar ratio of 2,6-DMN content in total DMN after isomerizationagainst 2,6-DMN content in total DMN before isomerization. According tothe present invention, this ratio can be more than 1.5.

By the way, the ratio between 2-MN and 1-MN is desired to be as high aspossible because higher 2-MN/1-MN ratio gives higher 2,6-DMN yield atalkylation. Theoretically the ratio is said to be around 2.2, however,it is difficult to achieve such a high ratio in the conventionalprocess. According to the present invention, the ratio can he more than2.0 in the transalkylation and isomerization by using MCM-22.

The present invention also provides a process for producing DMN from afeedstock comprising MMN and an alkylating agent with the catalystMCM-22, and MMN of the feedstock is the separated MMN of the product bythe transalkylation and isomerization. In this alkylation, the molarratio of 2,6-dialkylnaphthalene/2,7-dialkylnaphthalene of the alkylatedproduct can be more than 1.1.

Furthermore, the present invention provides a process for producing2,6-DMN from a feedstock comprising isomers of DMN and naphthalene bycontacting the feedstock with the catalyst MCM-22, comprising

step I step for transalkylation between isomers of DMN and naphthaleneto produce monomethylnaphthalene(MMN), and isomerization of DMN!,

step II step for separation of the product in said step I intonaphthalene, MMN and DMN!,

step III step for methylation of MMN fraction from step II usingmethylating agent to produce DMN!,

step IV step for separation of the product in said step III into MMN andDMN!,

step V step for separation of 2,6-DMN from mixture of DMN fraction insaid step II and said step IV!.

In this process, as illustrated in FIG. 1, naphthalene fraction in stepII recycles to step 1, MMN fraction in step IV recycles to step III, DMNfraction after separated 2,6-DMN therefrom in step V recycles to step I.

As a method for separation of step II or step IV, distillation can beemployed. To make this system simpler, step II and step IV can becombined as a single step by recycling the product of step III to stepII.

As for separation of step V, any method for separation of isomers suchas cooling crystallization or adsorption can be used. However, to obtainhigh yield of 2,6-DMN, High Pressure Crystallization is preferable.

Preferred alkylating agents include alcohols, olefins, aldehydes,halides, and ethers, such as methanol, dimethylether, polyalkylbenzene.Especially preferred is methanol.

The alkylation can be carried out in any of the known reactors usuallyemployed for alkylation. For example, a tubular reactor with a downflowof reactants over a fixed bed of catalyst can be employed.

The present invention will now be explained referring to examples.

EXAMPLE 1

(transalkylation and isomerization)

30 grams of MCM-22 (1/4"D×3/8"L, cylindrical pellet) are charged in atubular reactor (volume: 122 cc). The reactor was heated from roomtemperature to 400° C. at the rate of 100° C./hr over introducingnitrogen gas into the reactor at atmospheric pressure.

As a feedstock for transalkylation and isomerization, isomers of DMN andnaphthalene were used mixing DMN and naphthalene by 1:1 at molar ratio.Weight % of isomers of DMN is shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        (feedstock)                                                                   component              weight %                                               ______________________________________                                        dimethylnaphthalene    99.70                                                  2,6-DMN                6.21                                                   2,7-DMN                8.63                                                   other isomers          84.86                                                  monomethylnaphthalene  0.30                                                   2-MN                   0.17                                                   1-MN                   0.13                                                   ______________________________________                                    

The feedstock was introduced into the reactor at the rate of 30 g/hr for8 hours, and obtained product was analyzed by gas chromatography. Theresult of the product is shown in Table 2 with the component of thereactant.

                  TABLE 2                                                         ______________________________________                                        (transalkylation and isomerization)                                                        before reaction                                                                        after reaction                                          ______________________________________                                        component (wt. %)                                                             *   dimethylnaphthalene                                                                          53.19      39.41                                               2,6-DMN        3.30       6.65                                                2,7-DMN        4.59       4.59                                                other isomers  45.30      28.17                                           *   monomethylnaphthalene                                                                        0.10       17.59                                               2-MN           0.01       12.16                                               1-MN           0.09       5.43                                            *   naphthalene    46.71      38.15                                           *   other component                                                                              0          4.85                                            evaluation                                                                    2,6-DMN/total DMN (%)                                                                        6.2 . . . 1                                                                              16.9 . . . 2                                        2,6-DMN/2,7-DMN                                                                              0.72       1.45                                                content of 2,6-DMN                                                                           --         2.73                                                (after/before): @1                                                            NL conversion (%)                                                                            --         18.3                                                DMN conversion (%)                                                                           --         25.9                                                produced MMN/  --         0.70                                                (converted DMN × 2): @2                                                 2-MN/1-MN      --         2.23                                                ______________________________________                                         (note)                                                                        @1 in the table means a ratio of 2/1 in 2,6DMN/total DMN.                     @2 is caluculated on molar basis.                                        

As can be seen from Table 2, the ratio of 2,6-DMN/2,7-DMN is over 1.2and the ratio of 2-MN/1-MN is over 2.0.

EXAMPLE 2

(transalkylation and isomerization)

The same experiment with Example 1 except the molar ratio between DMNand naphthalene is 5:1 was carried out. The result of the product isshown in Table 3 with the component of the reactant.

                  TABLE 3                                                         ______________________________________                                        (transalkylation and isomerization)                                                        before reaction                                                                        after reaction                                          ______________________________________                                        component (wt %)                                                              *   dimethylnaphthalene                                                                          84.37      65.91                                               2,6-DMN        5.22       11.39                                               2,7-DMN        7.28       7.42                                                other isomers  71.87      47.10                                           *   monomethylnaphthalene                                                                        0.17       13.81                                               2-MN           0.02       9.54                                                1-MN           0.15       4.27                                            *   naphthalene    15.46      12.65                                           *   other component                                                                              0          7.63                                            evaluation                                                                    2,6-DMN/total DMN (%)                                                                        6.2 . . . 1                                                                              17.3 . . . 2                                        2,6-DMN/2,7-DMN                                                                              0.72       1.53                                                content of 2,6-DMN                                                                           --         2.79                                                (after/before): @1                                                            NL conversion (%)                                                                            --         18.2                                                DMN conversion (%)                                                                           --         21.9                                                produced MMN/  --         0.41                                                (converted DMN × 2): @2                                                 MMN 2-MN/1-MN  --         2.23                                                ______________________________________                                         (note)                                                                        @1  in the table means a ratio of 2/1 in 2,6DMN/total DMN.                    @2  is caluculated on molar basis.                                       

As can be seen from Table 3, the ratio of 2,6-DMN/2,7-DMN is over 1.2and the ratio of 2-MN/1-MN is over 2.0.

EXAMPLE 3

(alkylation)

153 grams of MCM-22 were charged in the tubular reactor(volume:370 cc).As a feedstock for alkylation, 1-MN (purity 95.5%) and 2-MN (purity96.6%) were used, and mixed at the molar ratio of 2.2 of 2-MN/1-UN.Feedstock was supplied in the reactor (350° C) at the rate of 76.7 g/hrfor 4 hours. Thereafter, methanol was started to be supplied in thereactor at the rate of 17.3 g/hr and the reaction proceeded for 20hours. The obtained product was analyzed by gas chromatography, and theresult is summarized in Table 4.

                  TABLE 4                                                         ______________________________________                                        (alkylation)                                                                                before reaction                                                                        after reaction                                         ______________________________________                                        component (wt %)                                                              *   dimethylnaphthalene                                                                           0          35.45                                              2,6-DMN         0          5.12                                               2,7-DMN         0          4.44                                               other isomers   0          25.89                                          *   monomethylnaphthalene                                                                         98.66      41.16                                              2-MN            67.61      28.84                                              1-MN            31.05      12.32                                          *   naphthalene     0          0.19                                           *   other component 1.53       23.20                                          evaluation                                                                    2-MN/1-MN       2.2        2.3                                                MN conversion (%)                                                                             --         58.28                                              2,6-DMN/total DMN (%)                                                                         --         14.45                                              2,6-DMN/2,7-DMN --         1.16                                               ______________________________________                                    

As can be seen from Table 4, the ratio of 2,6-DMN/2,7-DMN is over 1.1and the ratio of 2-MN/1-MN is over 2.0.

EXAMPLE 4

(alkylation)

153 grams of MCM-22 were charged in the tubular reactor(volume:370 cc).The same feedstock as in Example 3 was used. Feedstock was supplied inthe reactor(400° C.) at the rate of 153.4 g/hr for 4 hours. Thereafter,methanol was started to be supplied in the reactor at the rate of 17.3g/hr and the reaction proceeded for 20 hours. The obtained product wasanalyzed by gas chromatography, and the result is summarized in Table 5.

                  TABLE 5                                                         ______________________________________                                        (alkylation)                                                                                before reaction                                                                        after reaction                                         ______________________________________                                        component (wt %)                                                              *   dimethylnaphthalene                                                                           0          5.05                                               2,6-DMN         0          0.52                                               2,7-DMN         0          0.37                                               other isomers   0          4.16                                           *   monomethylnaphthalene                                                                         98.66      89.01                                              2-MN            67.61      59.84                                              1-MN            31.05      29.17                                          *   naphthalene     0          0                                              *   other component 1.53       6.93                                           evaluation                                                                    2-MN/1-MN       2.2        2.1                                                MN conversion (%)                                                                             --         9.78                                               2,6-DMN/total DMN (%)                                                                         --         10.37                                              2,6-DMN/2,7-DMN --         1.42                                               ______________________________________                                    

As can be seen from Table 5, the ratio of 2,6-DMN/2,7-DMN is over 1.1and the ratio of 2-MN/1-MN is over 2.0.

EXAMPLE 5

(separation)

(1) high pressure crystallization

2,636 grams of DMN isomers were supplied into the high pressurecrystallizer (KOBELCO 3 L type), and separated 396 grams of 2,6-DMNcrystals (purity 92%) at the condition of 2000 kgf/cm² and 45° C. (2)cooling crystallization

Using vessel for crystallization (3 litter), 1,980 g of DMN isomers iscooled quickly from 50° C. to 40° C. over stirring slowly. Then, 0.5grams of seed crystal was charged and kept the temperature at 40° C. foran hour. Thereafter, the feedstock was cooled to 10° C. at 2° C./min.29.7 grams of 2,6-DMN crystals (purity 80%) was separated by filtrationunder pressure.

The results of separation by both of high pressure crystallization andcooling crystallization are summarized in Table 6.

                  TABLE 6                                                         ______________________________________                                        (separation)                                                                  ______________________________________                                        HIGH PRESSURE CRYSTALLIZATI0N                                                 component     before                                                          (grams)       crystallization                                                                            crystal filtrate                                   ______________________________________                                        2,6-DMN       528          364     164                                        2,7-DMN       405          32      373                                        other DMN     1,703        0       1,703                                      TOTAL         2,636        396     2,240                                      2,6-DMN/2,7-DMN                                                                             1.3                  0.4                                        2,6-DMN/total DMN                                                                           20.0                 7.3                                        purity of crystal                                                                           --           92%     --                                         recovery of 2,6-DMN                                                                         --           69%     --                                         yield of 2,6-DMN                                                                            --           13.8%   --                                         ______________________________________                                        COOLING CRYSTALLIZATI0N                                                       component     before reaction                                                 (grams)       crystallization                                                                            crystal filtrate                                   ______________________________________                                        2,6-DMN       396          237.6   158.4                                      2,7-DMN       305          59.4    245.6                                      other DMN     1,286                1,286                                      T0TAL         1,987        297     1,690                                      2,6-DMN/2,7-DMN                                                                             1.3          0.6                                                2,6-DMN/total DMN                                                                           19.9                 9.4                                        purity of crystal                                                                           --           80%     --                                         recovery of 2,6-DMN                                                                         --           60%     --                                         yield of 2,6-DMN                                                                            --           11.9%   --                                         ______________________________________                                         (note)                                                                        "recovery of 2,6DMN" means the rate of 2,6DMN content in crystal against      of 2,6DMN content in feedstock.                                               "yield of 2,6DMN" means the rate of 2,6DMN content in crystal against of      total weight of feedstock.                                               

As shown in Table 6, yield of 2,6-DMN by high pressure crystallizationis much higher than by cooling crystallization. Further,2,6-DMN/total-DMN of the filtrate by high pressure crystallization isless than 8%. Therefore, the filtrate is more effective as a feedstockfor transalkylation and isomerization of 2,6-poor-DMN. Furthermore, whenthe purity of crystal was tried to increase in cooling crystallization,the yield of 2,6-DMN was lowered drastically.

What is claimed is:
 1. A process of preparing a polyester resincomprising:1) oxidizing 2,6-dimethylnaphthalene to form2,6-naphthalenedicarboxylic acid; and 2) manufacturing a polyester resinfrom said 2,6-naphthalenedicarboxylic acid, wherein said2,6-dimethylnaphthalene is prepared from a feedstock comprising isomersof dimethylnaphthalene and naphthalene comprising:I) transalkylatingisomers of dimethylnaphthalene and said naphthalene to producemonomethylnaphthalene; and isomerizing isomers of dimethylnaphthalene toproduce a dimethylnaphthalene isomerizate; II) separating the product ofstep I) into fractions of naphthalene, monomethylnaphthalene anddimethylnaphthalene; III) alkylating said fraction ofmonomethylnaphthalene of step II) with an alkylating agent to producedimethylnaphthalene; IV) separating the product of step III) intofractions of monomethylnaphthalene and dimethylnaphthalene; and V)separating 2,6-dimethylnaphthylene from said fractions ofdimethylnaphthalene of steps II) and IV), wherein steps I) and III) areeach conducted in the presence of a catalyst composition comprising asynthetic zeolite characterized by an X-ray diffraction patternincluding interplanar d-spacing
 12. 36±0.411.03±0.2 8.83±0.14 6.18±0.126.00±0.10 4.06±0.07 3.91±0.07 3.42±0.06 Å.
 2. The process of claim 1,wherein said feedstock comprises less than 11 weight % of2,6-dimethylnaphthalene in said isomers.
 3. The process of claim 1,wherein monomethylnaphthalene is produced at a molar ratio of2-monomethylnaphthalene/1-monomethylnaphthalene of more than 2.0.
 4. Theprocess of claim 1, wherein a product molar ratio of2,6-dimethylnaphthalene /2,7-dimethylnaphthalene is more than 1.2. 5.The process of claim 1, wherein a molar ratio of 2,6-dimethylnaphthaleneafter isomerization/2,6-dimethylnaphthalene before isomerization is morethan 1.5.
 6. The process of claim 1, further comprising separating saidmonomethylnaphthalene.
 7. The process of claim 6, further comprisingcontacting said monomethylnaphthalene with an alkylating agent and analkylation catalyst composition to produce an alkylate containing2,6-dimethylnaphthalene,wherein said alkylation catalyst compositioncomprises a synthetic zeolite characterized by an X-ray diffractionpattern including interplanar d-spacing12.36±0.4 11.03±0.2 8.83±0.146.18±0.12 6.00±0.10 4.06±0.07 3.91±0.07 3.42±0.06 Å.
 8. The process ofclaim 7, wherein said alkylate has a ratio of 2,6-dimethylnaphthalene/2,7-dimethylnaphthalene of more than 1.1.